Broadcasting is the typical mechanism to allow all devices in a wireless communication systems, within the radio coverage area of a transmitting device, to learn/retrieve relevant information necessary for properly performing network functions. In a central-control type system, the coordinator, also referred to as a controller, or access point, is the device responsible for sending beacon packets to accomplish this function. Beacon packets contain information, such as network timing, reservations of channel time allocation, and other essential network information under control of the coordinator.
This approach works well in a simple network, wherein one controller controls all devices operating on the network, and any additional devices which join the network. It also works well when the network is deployed in an infrastructure scenario, e.g., wherein any device is guaranteed to find the beacon packets from at least one access point (AP). However, correct and adequate operation is problematic when a network is configured in an ad hoc manner, wherein the overall network topology changes dynamically. In an ad hoc network, a device may not necessarily be in a coverage area of the beacon-sending coordinators. There may also be occasions when multiple networks operate simultaneously, with overlapping coverage areas because of close proximity of the coordinators. In the former case, a device may not be able to find the required network resources for its intended application; in the latter case, coexistence and optimized use of radio resources among the involved networks may not be possible. Both cases likely occur in home networking environments, wherein devices are deployed without pre-planning, and wherein applications need to support plug-and-play with little user intervention. Moreover, portable devices and/or complicated layout configurations cause dynamic network topology because of changing radio coverage.
Existing wireless systems rely on a centralized topology for maintaining the clock/timing of networks for device synchronization. This task is normally achieved by one designated device which repeatedly sends beacon signals according to a pre-determined interval, referred to as a “superframe.” Because the beacons occur periodically, other devices may either acquire access to the network by sensing the presence of a beacon, or may simply maintain synchronization by referencing the starting point of each beacon. There are various names for the device responsible for beacon transmissions, e.g., access point in 802.11 WLAN (AP), coordinator in 802.15.3 piconet (PNC) (IEEE Std 802.15.3™-2003, Part 15.3: Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications for High Rate Wireless Personal Area Networks (WPANs)), controller, or master, in some TDMA type networks. In the following descriptions, the term “PNC” is used generally, however, the scope of this invention is not limited to that of IEEE 802.15.3 WPAN protocols, and is applicable to any network protocol so long as the mechanism of maintaining superframe and/or beacon timing are the same or similar to that of IEEE 802.15.3, and channel time allocation is made via request/grant reservation to/from the coordinator.
Referring now to FIGS. 1 and 2, a typical network configuration, e.g., a piconet, of consideration and the associated timing chart of packet exchange among PNC/devices, respectively, is depicted generally at 10 in FIG. 1. Solid arrows 12, 14, indicate the direction of packet transmissions. As previously mentioned, PNC 16 is responsible for sending beacons. Both Dev#1 & Dev#2 receive beacons from PNC and decode them to retrieve timing information. To facilitate traffic for user applications, one or more reservations (Res—dotted arrows 18, 20) may be setup, as long as there is available time in the superframe for PNC 16 to allocate them. In general, each reservation includes one or more dedicated time slots for a pair of devices, e.g., Res#1 18, or between PNC and a device, e.g., Res#2 20. In either case, request of the reservation goes through negotiation with PNC 16. The reservation request/negotiation process is not a part of this invention; an example may be found in IEEE 802.15.3 WPAN Standard. Once a reservation is granted, two devices can communicate to each other in the designated time slot, without contention from other devices in the piconet.
U.S. Pat. No. 6,665,311, for Method and apparatus for adaptive bandwidth reservation in wireless ad-hoc networks, to Kondylis et al., granted Dec. 16, 2003, describes a routing technique which separates the signaling and data transmission portions of a data frame. The data portion also includes a reservation confirmation portion which allows reservations made during the signaling portion of the frame to be confirmed immediately prior to transmission of the data.
U.S. Pat. No. 6,507,587, for Method of specifying the amount of bandwidth to reserve for use in network communications, to Bahl, granted Jan. 14, 2003, describes a system wherein a reservation is performed by dividing the communication channel into a plurality of frames, dividing each of the frames into a plurality of slots, and dividing some of the plurality of slots into a plurality of mini-slots. The mini-slots are provided for use by the multiple communication sources to request the establishment of a new voice, data, or video transmission connection over the communication channel.
U.S. Pat. No. 6,349,210, for Method and apparatus for broadcasting messages in channel reservation communication systems, to Li, granted Feb. 19, 2002, describes a system for reliable multicast data transmission. It utilizes redundant Request-to-Send type or broadcast notice messages or packets. A source node repeatedly transmits a sequence of these messages over a system reservation channel with each message containing a sequence identifier. The receiving nodes determine the commencement of broadcasting data by recognizing the last broadcast notice message in the sequence.
U.S. Pat. No. 6,104,712, for Wireless communication network including plural migratory access nodes, to Roberts et al., granted Aug. 15, 2000, describes a distributed access network achieved by providing plural migratory, or roving, access nodes to populate a region of desired service, optionally determining a node-to-node route between a source and destination, and initiating a data transfer between the source and destination by way of the migratory nodes.
U.S. Patent Publication No. 20030199279, for Method of accommodating overlapping or adjacent networks, of Robert et al., published Oct. 23, 2003, describes a system where avoidance of interference in a WPAN is achieved initially in a PHY layer (code set changes) and, subsequently in a MAC layer (merging piconets). The approach used for merging piconet relies on detecting beacons and having two piconets within range of each other.
WO0239665 for Coordinated inquiry and page procedures in an ad-hoc wireless network, of Rune, published May 16, 2002, describes a method by which a central controller manages subordinate networks. The reference presumes connections exist among all controllers.
EP1207654A2, for Coexistence techniques in wireless networks, of Shellhammer et al., published May 22, 2002, describes provision of techniques for frequency coordination among two different wireless network protocols, operating in close proximity with one another. Coordination is accomplished by the use of a coordinator associated with the base station for, in turn, activating the first radio transceiver, deactivating the first radio transceiver, activating the second radio transceiver, and deactivating the second radio transceiver. The coordinator in this reference is physically attached to both radio transceivers.
WO0165773A2, for Scheme for managing overlapping wireless computer networks, of Gubbi et al., published Sep. 7, 2001, describes a scheme for sharing a channel during a contention free period of communications between two or more basic service sets (BSSs), including network components, in an overlapping region of a wireless computer network. The reference uses point coordinators, which are stationary rather than portable. A proxy coordinator of the reference needs to be identified for broadcasting beacons in the overlapped area.
WO2002063806 A2 for System, method, and computer program product for sharing bandwidth in a wireless personal area network or a wireless local area network, of Shvodian, published Aug. 15, 2002, describes an access scheme wherein devices share bandwidth via the same coordinator, in a simple, i.e., one, piconet scenario.